輕量化設(shè)計(jì)的汽車零部件用高強(qiáng)度鋼來抗凹外文文獻(xiàn)翻譯、中英文翻譯

輕量化設(shè)計(jì)的汽車零部件用高強(qiáng)度鋼來抗凹外文文獻(xiàn)翻譯、中英文翻譯,量化,設(shè)計(jì),汽車零部件,強(qiáng)度,鋼來抗凹,外文,文獻(xiàn),翻譯,中英文 輕量化設(shè)計(jì)的汽車零部件用高強(qiáng)度鋼來抗凹 張研 來新民 朱平 王吳榮 摘要 輕巧耐撞性是汽車車身設(shè)計(jì)的兩個(gè)重要因素。在這篇文章中，基于淺殼理論，表達(dá)抗凹剛度的雙曲率扁殼是在集中載荷條件下取得的。該臨界負(fù)荷導(dǎo)致當(dāng)?shù)噩嵥榈陌己墼谠撝行牡臏\殼被視為輕量級(jí)對(duì)汽車零部件的重要影響指數(shù)。本規(guī)則適用于輕量化設(shè)計(jì)的保險(xiǎn)杠系統(tǒng)用高強(qiáng)度鋼代替溫和鋼。耐撞模擬輕量級(jí)的一部分，證明了輕量化進(jìn)程的有效性。 關(guān)鍵詞: 高強(qiáng)度鋼 輕量 抗凹 1、介紹 近年來，由于汽車保有量的急劇增長，大大影響了社會(huì)和人們的生活，這種情況帶來了很多嚴(yán)峻的問題比如能源危機(jī)，環(huán)境污染。國際鋁組織協(xié)會(huì)聲明石油的消耗可降低8-10％與減少約10％的汽車重量。因此，汽車輕量化是節(jié)約燃料的一個(gè)基本方式。 為了減少汽車的重量，這又兩個(gè)較好的方法。一種方法是重新設(shè)計(jì)汽車零部件優(yōu)化其結(jié)構(gòu)，通過使用細(xì)薄的、空心的、小型的和混合材料的零部件，來減輕汽車的重量。另一種是使用新的輕型材料，如今這種材料越來越多，如鋁合金，高強(qiáng)度鋼，復(fù)合材料都被廣泛作為輕質(zhì)材料以取代傳統(tǒng)材料如低碳鋼。這些材料可以顯著的減輕汽車的重量。使汽車輕量化材料替換比優(yōu)化結(jié)構(gòu)更有效。根據(jù)引進(jìn)的汽車安全法規(guī)，輕量化設(shè)計(jì)的車身中耐撞性和安全性被視為先決條件。高強(qiáng)度鋼被廣泛的應(yīng)用于汽車上以代替?zhèn)鹘y(tǒng)的低碳鋼。 高強(qiáng)度鋼板可用于汽車車身來提高部件碰撞能量吸收能力和耐塑性變形能力。汽車體重可減少通過使其零部件用一個(gè)更薄厚度的高強(qiáng)度鋼板取代低碳鋼板來制造。與鋁相比，鎂，復(fù)合材料和高強(qiáng)度鋼具有更好的經(jīng)濟(jì)性因?yàn)檫@些材料的原料和制作費(fèi)用比較便宜。此外，高強(qiáng)度鋼可直接應(yīng)用到生產(chǎn)線上，包括成型，焊接，裝配和油漆。經(jīng)營成本節(jié)省了，因?yàn)闆]有必要對(duì)整個(gè)線路進(jìn)行調(diào)整。 在車身外，有幾個(gè)薄的金屬板，其中大部分是淺水面板。凹痕阻力是有能力保持形狀對(duì)沉沒撓度和地方凹痕在外力的作用下。凹性汽車板成為汽車的一個(gè)重要方面和質(zhì)量標(biāo)準(zhǔn)。因此，抗凹剛度的汽車板應(yīng)在面板設(shè)計(jì)和制造過程中被測(cè)試和評(píng)估。一些報(bào)道的測(cè)試方法列舉如下: 1）、在外力不變的情況下，測(cè)量位移沉沒撓度的fp 2）、測(cè)試外力F到獲得固定位移沉沒偏轉(zhuǎn)量 3）、在外力載荷作用下測(cè)試得邊坡力位移曲線 在這篇文章中，第二種方法將被采用，該表達(dá)抗凹剛度雙曲率淺殼是通過淺殼理論和集中負(fù)載的條件下得到的。該臨界負(fù)荷導(dǎo) 致該中心淺殼瑣碎的凹痕被視為凹性汽車零部件的重要評(píng)價(jià)指數(shù)。本規(guī)則適用于在第2條中，輕量化設(shè)計(jì)連年系統(tǒng)用高強(qiáng)度鋼代替低碳鋼與耐撞性仿真。 2、雙曲率淺殼的抗凹性分析 2.1 淺殼的抗凹剛度分析 殼牌與中表面特點(diǎn)可以分為三特征：厚度h，中面尺寸L，曲率半徑r ，并滿足的h / r<<1。當(dāng)h/L<<1時(shí)，定義外殼為薄殼，如果在上述兩條件滿足的同時(shí)又滿足L／r<<1，這個(gè)薄殼被認(rèn)為是淺殼。 如圖1所示，平面x-y是淺殼中表面沿著z軸的投影。假設(shè)M是中表面上的任意一點(diǎn)，兩平面QMN&PMN分別去平行OYZ和OXZ。邊PM和QM可近似認(rèn)為是垂直的因?yàn)橹斜砻婧推教?。同時(shí)，MN正交于中面。因此，MN,PM,QM可構(gòu)成垂直參考系MPQN。其差額由正交坐標(biāo)系統(tǒng)OXYZ可以忽略不計(jì)，同時(shí)PM和QM通過α和β來表示，該曲面坐標(biāo)MPQN。 圖1 假設(shè)M是Z軸上的一點(diǎn)，對(duì)中表面的詳細(xì)分析方程如下： z=F(x,y) （1） 由于是平坦的外殼，就有如下方程： （2） 中面的曲率和撓度可近似至： （3） 該中面的下載系數(shù)可沿α和β方向?qū)С觯? （4） 運(yùn)用集中力P沿Z軸和忽略橫向剪切力造成的影響，得到淺殼的平衡微分方程： （5） 其中δ（0，0）是狄拉克-δ函數(shù)。 淺殼的兼容性方程是： （6） 其中 通過橫向位移w來表達(dá)瞬時(shí)結(jié)果M1, M2和M12，淺殼在橫向集中力下的基本方程： （7） 其中N1是膜應(yīng)力在X方向，N2是膜應(yīng)力在Y方向，D表示淺殼的抗彎剛度。 這是很難解決上述方程。據(jù)要立足現(xiàn)實(shí)，沉沒的偏轉(zhuǎn)將只集中就在小范圍內(nèi)左右對(duì)外力P ，所以無限大型淺水殼牌是假定在這項(xiàng)研究中。因?yàn)閣，N1,N2關(guān)于X,Y軸對(duì)稱，所有順序衍生的w,N1,N2都無限接近于零，以下方程可通過傅立葉進(jìn)行變換。 （8） 其中： （9） 從公式（8）我們可以得到。通過逆向傅立葉變換和極坐標(biāo)轉(zhuǎn)換ξ,η,w，再根據(jù)極坐標(biāo)系統(tǒng)我們可以得到： （10） 把x=0,y=0帶入式（8），這關(guān)系在偏轉(zhuǎn)力fp和矩形淺殼的集中力P我們可以得到如下： （11） 最后抗凹剛度的雙曲率淺殼K便可獲得 (12) 這個(gè)等式綜合的說明了該抗凹剛度雙曲率淺殼的所有影響因素，包括材料性能，幾何參數(shù)，這些因素可以用來引導(dǎo)設(shè)計(jì)，材料選擇及制造。 2.2分析臨界載荷造成當(dāng)?shù)噩嵥榘己? 為定量評(píng)價(jià)的臨界載荷對(duì)地方抗凹的展板，幾位研究員已經(jīng)提出了經(jīng)驗(yàn)公式。根據(jù)大量的實(shí)驗(yàn)，Dicellello說明一個(gè)公式表明最低能量W造成有形瑣碎的凹痕微量由厚度T的屈服應(yīng)力RS和基本抗凹剛度K。 （13） 其中C是比例恒，從公式（12）和（13），臨界載荷聚合酶鏈反應(yīng)，導(dǎo)致淺殼中心瑣碎的凹痕是可以實(shí)現(xiàn)的，其中這被定義為評(píng)價(jià)。 （14） 從公式（14），是有密切相關(guān)關(guān)系臨界負(fù)荷Pcr和厚度t,屈服應(yīng)力,關(guān)鍵負(fù)載可以是根據(jù)一個(gè)規(guī)則進(jìn)行輕量化設(shè)計(jì)其中汽車零部件用高強(qiáng)度鋼代替低碳鋼。 3、舉列和耐撞性分析 3.1 整車的有限元模型及其碰撞模擬 一份詳細(xì)的有限元模型已確立基于從一輛房車改裝成一輛客車， 如圖2所示。以確保正確性性和有效性的有限元模型，一下方法將被采用： 1、因?yàn)槟康氖菫榱四M正面碰撞的車，嚙合的前端車身比后方車身更稠密。 2、采取4節(jié)點(diǎn)殼單元和8節(jié)點(diǎn)磚固體成分來降低集成方法與沙漏控制，以提高仿真效率。 3、用嚙合和大量的縮放技術(shù)，到該特征長度的最小單元以確保提高仿真效率。 4、材料本構(gòu)與Cowper–Symonds應(yīng)變率項(xiàng)目是用于鋼鐵零件。 5、自動(dòng)單面接觸算法是通過在模擬瞄準(zhǔn)的復(fù)雜性來進(jìn)行汽車碰撞仿真分析。 圖2 整車的有限元模型 6、點(diǎn)焊元件故障規(guī)則中說，考慮到該對(duì)標(biāo)準(zhǔn)力和剪切力，是用來模擬點(diǎn)焊連接汽車零部件。 顯式動(dòng)力有限元軟件LS - DYNA的950版本是用來模擬正面碰撞的車對(duì)剛性壁在車速為50公里/秒根據(jù)國家墜毀立法CMDVR294。一個(gè)真正的車毀人亡實(shí)驗(yàn)是在清華大學(xué)實(shí)驗(yàn)室做的汽車碰撞。通過對(duì)比時(shí)程加速度某些位置上的一個(gè)支柱0.1 s時(shí)，模擬給出了一個(gè)合理的適合實(shí)驗(yàn)結(jié)果，其中保證正確性的有限元模型，并給出了更好的基地，為下一步輕量化優(yōu)化設(shè)計(jì)做準(zhǔn)備。 3、2輕量化設(shè)計(jì)及耐撞性分析 使用高強(qiáng)度鋼，是其中一個(gè)有效的如何降低汽車重量。然而，部分績(jī)效（如耐撞性，剛度，抗凹）通過新的材料得到保證。舉例來說，前面部分的汽車是主要能源吸收部分，在這一過程中的車毀人亡，所以能源吸收性能不影響乘客，故設(shè)計(jì)的前車零件的安全性需得到保證。在這項(xiàng)研究中，研究了不同的材料來制作汽車的緩沖器，但其余的為抗凹。 低碳鋼及高碳鋼的力學(xué)性能如下（見表1）： 評(píng)價(jià)指標(biāo)的凹痕阻力保險(xiǎn)杠用低碳鋼是 （15） 當(dāng)高強(qiáng)度鋼是用來取代低碳鋼其余的主要形狀和抗凹性能， 高強(qiáng)度鋼的新厚度可以實(shí)現(xiàn) （16） 從公式（16）可以得到，保險(xiǎn)杠的厚度可使用高強(qiáng)度鋼得到積累和更新，在整車FE模型中。變形過程中的收獲，以新的材料取得后，車毀人亡的是重新模擬與更新部分厚度（見圖3） 圖3 通過模擬實(shí)驗(yàn)中，變形的保險(xiǎn)杠有兩種不同的材料相似，即塑料鉸鏈與張力塑性變形出現(xiàn)在部分保險(xiǎn)杠的中部。能量吸收的過程表現(xiàn)在保險(xiǎn)杠橫梁上。從圖 4可以看出兩種材料的能量吸收差異很小，約4.1 ％為保險(xiǎn)杠梁吸收。從中可以得出一個(gè)結(jié)論，在這份研究中說明的是在抗凹性的評(píng)價(jià)指標(biāo)的基礎(chǔ)上，合理的減少保險(xiǎn)杠板的厚度。 圖4 4、結(jié)論 本文研究了汽車中叫小的雙曲率淺殼的抗凹性零件，使用方法如下： 1、 抗凹剛度下，集中力量，是鑒于這種零件。 2、 臨界載荷導(dǎo)致當(dāng)?shù)噩嵥橄魅踉撝行牡臏\殼已推斷， 這反過來又成為汽車零部件凹痕阻力的評(píng)價(jià)指數(shù)。 3、 有效性的評(píng)價(jià)指標(biāo)，就是證明申請(qǐng)發(fā)達(dá)國家的規(guī)則向輕量化設(shè)計(jì)的保險(xiǎn)杠系統(tǒng)采用高強(qiáng)度鋼代替溫和鋼并通過耐撞性仿真 參考文獻(xiàn)： 【1】 李元先，林中勤，江愛琴，陳關(guān)龍，使用高強(qiáng)度鋼的輕量化設(shè)計(jì)與防撞車身，2003；24：177-82 【2】 李元先，汽車車身輕量化研究的基礎(chǔ)上耐撞性的數(shù)值模擬。博士論文，中國，上海交通大學(xué)，2003 【3】 朱石鋒，宋奇峰，解放1092汽車車身輕量的研究，汽車工藝材料，2002 【4】 Jambor A, Beyer M. 新汽車新材料，1997 【5】 Che on SS, Lee DG, Jeong KS. 復(fù)合材料門影響客車橫梁，1997 【6】 李忠勝，周先斌，汽車鋼板抗凹性的動(dòng)太靜態(tài)分析，2003 【7】 李忠勝，周先斌，雙曲率車身鋼板的下沉剛度，2003 【8】 對(duì)轎車車身鋼板的強(qiáng)度，剛度及抗凹性分析，1995 【9】 車身面板的抗凹性的設(shè)計(jì)標(biāo)準(zhǔn)，SAE 1974 【10】韓強(qiáng)，黃小清，恁建國，先進(jìn)的鋼板殼體理論，2002 Short communicationLightweight design of automobile component usinghigh strength steel based on dent resistanceYan Zhang*, Xinmin Lai, Ping Zhu, Wurong WangSchool of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200030, PR ChinaReceived 19 May 2004; accepted 14 September 2004AbstractLightweight and crashworthiness are two important aspects of auto-body design. In this paper, based on the shallow shell theory,the expression of dent resistance stiffness of double curvatured shallow shell is obtained under the concentrated load condition. Thecritical loads resulting in the local trivial dent in the center of the shallow shell is regarded as the important index for the lightweightof the automobile parts. This rule is applied to the lightweight design of bumper system by using high strength steel instead of mildsteel. The crashworthiness simulation of the lightweight part proves the validity of the lightweighting process.? 2004 Elsevier Ltd. All rights reserved.Keywords: High strength steel; Lightweight; Dent resistance1. IntroductionIn recent years, the retaining number of automobileshas been increasing steadily, which has impacted thesociety and human life greatly. Such situation leads tomany severe problems such as fuel crisis, environmentpollution. The international association of aluminumstated that petrol consumption can decrease by 810%with 10% reduction of car weight 2. Thus, automobilelightweight is a basic way to fuel saving.In order to reduce the automobile weight, there aretwo important methods 3: One, automobile parts areredesigned to optimize the structure. By using thinning,hollowing, minitype, and compound parts, car weightcan be reduced. The other, more and more lightweightmaterials, such as aluminum alloy, high strength steel,composite material, are widely used as lightweight mate-rials to replace the traditional materials like mild steel4. These materials could reduce the weight remarkably.Material replacement is generally more effective in auto-mobile lightweighting than structure modification. Withthe introduction of automobile safety legislation, crash-worthiness and safety should be considered as precondi-tions in lightweighting design of auto-body.High strength steel is widely used in automobilereplacing the traditional material of mild steel. Highstrength steel sheet can be used in auto-body to improvecomponents? impact energy absorption capacity andresistancetoplasticdeformation.Theautomobileweight can be reduced by use of high strength steel sheetof a thinner thickness to replace the mild steel sheet ofbody parts 1,3. Comparing with aluminum, magne-sium, and composite materials, high strength steel hasbetter economy in that its raw material and fabricationcost are cheaper. Besides, high strength steel can be di-rectly used in product line including forming, wielding,assembling, and painting. The operating cost can besaved since there is no need adjusting the whole line.Outside of automobile body, there are several sheetmetal Panels, most of which are shallow panels. Dentresistance is the ability to retain the shape against sunkendeflection and local dent under the external force. Dent0261-3069/$ - see front matter ? 2004 Elsevier Ltd. All rights reserved.doi:10.1016/j.matdes.2004.09.010*Corresponding author. Tel.: +86 21 62932964; fax: +86 2162933093.E-mail address: (Y. Zhang) and Design 27 (2006) 6468Materials& DesignResistance of automobile panels becomes an importantissue and quality criterion. Therefore, dent resistancestiffness of automobile panels should be tested and eval-uated in the process of panel design and manufacture.Some reported methods of testing are listed below 68:1. Test the displacement of sunken deflection fpunderfixed external force.2. Test the external force f to obtain fixed displacementof sunken deflection.3. Test the slope of forcedisplacement curve underexternal load.In this study, the second method will be used. The restof this paper is organized as follows: In Section 2, theexpression of dent resistance stiffness of double curva-tured shallow shell is obtained under the concentratedload condition based on the shallow shell theory. Thecritical load resulting in the local trivial dent in the centerof the shallow shell is regarded as the important evaluat-ing index for the dent resistance of the automobile parts.This rule is applied in Section 2 to the lightweighting de-sign of bumper system by using high strength steel in-stead of mild steel with crashworthiness simulation.2. Dent resistance analysis of double curvatured shallowshell2.1. Dent resistance stiffness analysis of shallow shellShell with mid surface can be characterized into threefeatures: thickness h, mid surface dimension L, curva-ture radius r, which satisfies h/r ? 1. When there existsh/L ? 1, the shell can be defined as thin shell. If L/r ? 1 is added besides the above two conditions, thethin shell is regarded as shallow shell 10.As Fig. 1 shows, the plane xy is the projection of themid surface of shallow shell along the z-axis. SupposingM is an arbitrary point on mid surface, two planesQMN & PMN are made paralleling to coordinate planeOYZ and OXZ, respectively. The two edges PM andQM can be regarded approximately as vertical becauseof mid surface?s flatness. At the same time, the lineMN is normal to mid surface. Thus, MN, QM, PMcan constitute a perpendicular reference frame MPQN,whose difference from orthogonal coordinate systemOXYZ can be ignored. And PM and QM are denotedby a and b, the curvilineal coordinate of MPQN.Assuming the Z coordinate of the point M is z, theanalytical equation of mid surface is expressed asfollows:z Fx;y:1The following equations can be obtained because of theflatness of the shell:ozox?2? 1;ozoy?2? 1;ozox?ozoy? 1:2The curvature and torsion of mid surface can be approx-imated to:kx ?o2zox2;ky ?o2zoy2;kxy ?o2zoxoy:3The Lae coefficients of mid surface along a and b direc-tions are deduced:A ds1dadxdx 1;B ds2dbdydy 1:4Applying concentrated force P along Z-axis and ignor-ing the influence of the transverse shear resultant forces,the balance differential equations of shallow shell are:oN1oxoSoy 0;oN2oyoSox 0;?kxN1 kyN2 oQ1oxoQ2oy Pd0;0 0;5Q1oM12oyoM1ox; Q2oM12oxoM2oy;where d(0,0) is Dirac-d function.The compatibility equation of shallow shell isr2N1 N2 ? Etr2kw 0;6where r2o2ox2o2oy2; r2k kxo2ox2 kyo2oy2:Expressing the moment resultants M1, M2and M12by the function of transverse displacement w, the basicequations of shallow shell under concentrated transverseforces are:Dr2r2w kxN1 kyN2 Pd0;0;r2N1 N2 ? Etr2kw 0;o2N1ox2o2N2oy2;7where N1is the membrane stress resultant in X-direc-tion; N2, the membrane resultant in Y-direction; D, thebending stiffness of shallow shell.Fig. 1. Double curvature shallow shell.Y. Zhang et al. / Materials and Design 27 (2006) 646865It is very difficult to solve above equation. Accordingto practical situation, sunken deflection will only con-centrate on a small area around external force P, so infi-nite large shallow shell 5 is assumed in this study.Because w, N1, N2are symmetric about x-, y-axis, all or-ders of derivatives of w, N1, N2become to zero at infin-ity. The following equations can be achieved by Fouriertransformation to Eq. (7):Dn2 g2 w kxN1 kyN2 P;n2 g2N1N2 ? Etkyn2 kxg2 w 0;n2N1 g2N2;8where:Z1?1Z1?1Pd0;0e?inxe?igydx dy P; w 4Z10Z10wcosnxcosgydx dy;N1 4Z10Z10N1cosnxcosgydx dy;N2 4Z10Z10N2cosnxcosgydx dy:9From Eq.(8), w can be obtained. Reverse Fourier trans-formation to w and polar coordinates transformation ton, g, w under polar coordinate system can be gainedw Pp2DZp=20Z10qcosqxcoshcosqy sinhq412t2kxcos2h kysin2h2dq dh;10Put x = 0 and y = 0 in Eq.(8), the relationship betweendeflection fpand concentrated force P of rectangle shal-low shell can be achieved as follows:P 4Et2ffiffiffiffiffiffiffiffiffikxkyp1 ? l2ffiffiffi3pfp:11Finally, dent resistance stiffness of shallow shell K isobtainedK Pfp4Et2ffiffiffiffiffiffiffiffiffikxkyp1 ? l2ffiffiffi3p :12This equation explains synthetically the relationship be-tween the dent resistance stiffness of double curvatureshallow shell and all influencing factors including mate-rial properties, geometry parameters, which can be usedto guide design, material select and manufacture.2.2. Analysis of critical load causing local trivial dentFor quantitative evaluation of critical load against lo-cal dent resistance of panels, several experience formulashave been brought forward by researchers. Based onlarge numbers of experiments, Dicellello 9 stated a for-mula that expresses minimum energy W causing visibletrivial dent trace by thickness t, yield stress rsand basicdent resistance stiffness KW Cr2st4K;13where C is proportional constant. From Eqs. (12) and(13), the critical load Pcrresulting in the local trivial dentin the center of the shallow shell can be achieved, whichis defined as the evaluating indexPcr Crst2:14From Eq. (14), there is a closely correlation betweencritical loads Pcrand thickness t, yield stress rs. The crit-ical load can be a rule to carry out lightweight design ofautomobile parts by using high strength steel instead ofmild steel.3. Example and crashworthiness analysis3.1. FE model of full car and its crash simulationA detailed finite element model has been establishedbased on a passenger car refitted from a saloon car,which is showed in Fig. 2. To ensure the correctnessand effectiveness of FE model, the following methodsare adopted:1. Since the goal is to simulate the frontal impact of thecar, the meshing of front car body is denser than thatof the rear car body.2. Reduced integration method with hourglass control istaken for 4 noded shell element and 8 noded bricksolid element to improve the efficiency of simulation.3. By using of the meshing and mass scaling technology,the characteristic length of the minimal element isensured to improve the simulation efficiency.4. Materials constitutive with CowperSymonds strainrate item is used for steel parts.5. Automaticsinglesurfacecontactalgorithmisadopted in the simulation aiming at complexity ofcar impact simulation.Fig. 2. Finite element model of full car.66Y. Zhang et al. / Materials and Design 27 (2006) 64686. Spot weld element with failure rule that consideringthe couple of normal force and shear force is used tosimulate the spot weld connection between auto parts.Explicit dynamic FEM software LS-DYNA Version950isusedtosimulatethefrontalimpactofthecaragainsta rigid wall at the speed of 50 km/s according to the Na-tional Crash Legislation CMVDR294. A real car crashexperiment is done at Car Crash Lab settled in TSingHuaUniversity.Bycomparingthetimehistoryofacceler-ation of certain position on the A pillar within 0.1 s, thesimulationgivesareasonablefittotheexperimentresults,which guaranteesthecorrectness ofFEmodel andgives anicer base for the next lightweighting optimized design.3.2. Lightweighting design and crashworthiness analysisThe use of high strength steel is one of the effectiveways to reduce car weight. However, the performance(such as crashworthiness, stiffness, and dent resistance)of part made of new material should be assured. Forexample, the front parts of a car are major energyabsorption parts in the process of car crash, so energyabsorption performance without affecting the safety ofpassengers should be assured in the design of front partsof a car. In this research, the bumper of the passengercar is studied under different materials but remainingits dent resistance.The mechanical properties of mild steel and highstrength steel are listed below (see Table 1).The evaluation index of dent resistance for bumperusing mild steel isPcr1 C1rs1t21:15When high strength steel is used to replace the mild steelremaining its primary shape and dent resistance per-formance, the new thickness t2of high strength steelcan be achievedt2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiC1rs1C2rs2t1r:16From (16), the thickness of bumper that uses highstrength steel is gained and updated in the full car FEmodel. The deformation history of bumper using newmaterial is achieved after the car crash is re-simulatedwith updated part thickness (see Fig. 3).By simulation, the deformations of bumper made oftwo different kinds of material are similar in that plastichingeandtensionalplasticdeformationappearinthemid-dle part of bumper. And the energy absorption history isshown in the following for beam of the bumper. FromFig. 4 the difference of the energy absorption betweenTable 1Mechanical properties of two materialsMaterialDensity (g/cm3)E (GPa)lrs(MPa)Mild steel7.82100.3166High strength steel7.82100.3220Fig. 3. The deformation history of bumper using high strength steel.Fig. 4. Energy absorption time history of bumper beam.Y. Zhang et al. / Materials and Design 27 (2006) 646867twomaterialsissmall,about4.1%forbeamofthebumper,from which a conclusion can be drawn that itis feasible toreducethethicknessofthebumperpanelbasedonthedentresistance evaluation index studied in this research.4. ConclusionDent resistance performance of small curvature shal-low shell parts in automobile is studied in this paper,which enables the follows:1. Dent resistance stiffness under concentrated force isgiven for such parts.2. The critical load resulting in the local trivial dent inthe center of the shallow shell has been deduced,which in turn becomes the index to evaluate the dentresistance of automobile parts.3. The validity of evaluating index is proven by applyingthe developed rule to the lightweight design of bum-per system using high strength steel instead of mildsteel through crashworthiness simulation.References1 Yuxan Li, Zhongqin Lin, Aiqin Jiang, Guanlong Chen. Use ofhigh strength steel for lightweight and crashworthy car body.Mater Des 2003;24:17782.2 Yuxuan Li. Automobile body lightweighting research based oncrashworthiness numerical simulation. PhD thesis, Shanghai JiaoTong University, China; 2003.3 Zhu Shi-feng, Song Qi-feng. Research of CA1092 automotivebody lightening. 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